The present invention relates to a standby supply system for delivering pressure fluid to a user component, in particular a hydraulic brake booster, with a primary fluid source adapted to be connected to the user component through a valve arrangement, and with a secondary fluid source adapted to be connected to the user component through the valve arrangement in the event of failure of the primary fluid source.
Such a standby supply system is known from German Printed Application DE-OS No. 2,043,963 in which both fluid sources are pumps. In the normal operating state, the primary pump delivers fluid to the user component through a supply line while the fluid delivered by the secondary pump is passed to the unpressurized reservoir. If the delivered fluid volume drops or the primary pump fails, the secondary pump is connected to the supply line which communicates with the user component, supplying the user component with pressure fluid.
This standby supply system serves to provide continued flow of fluid, corresponding to the delivery of the primary pump, to the user component in the event of failure of the primary pump. This makes it necessary to provide a secondary fluid source which is just as costly as the primary fluid source. Thus, two pumps and two pump drives are required.